The present invention relates to an optical receiver to receive an optical signal using visible light and more particularly to a technology effectively applied to an optical communication system that superimposes an optical modulation signal on LED (Light Emitting Diode) illuminating light to perform data communication.
Recently, the visible light communication technology using LED illumination has developed to cause increasing use of an apparatus that superimposes an optical modulation signal on visible light to perform data communication. For example, patent literature 1 describes the optical receiver applicable to the visible light communication. According to the description, a bandpass filter is used to extract frequency components from an electric signal output from a light receiving element (photodiode). An A/D converter is used to demodulate the signal. The described technology features “the direct-current component elimination process” and “the AGC amplification factor control.” The technology extracts a direct-current component contained in an output signal from a first-stage amplifier, feeds a bias current back to an input side of the first-stage amplifier to cancel the direct-current component, and eliminates the direct-current component supplied to the first-stage amplifier. The technology applies a bias current to cancel a direct-current component so as to be able to eliminate the direct-current component from an electric signal applied to the first-stage amplifier and increase an amplification factor of the first-stage amplifier. This enables to receive a weak optical modulation signal and increase a dynamic range to receive optical modulation signals. The technology controls adjustment of a variable gain amplifier (AGC amplification factor control) only when a signal preamble is received, not always, to shorten the time to adjust the AGC amplification factor.
Patent literature: Japanese patent laid-open No. 2013-5327